1. Field of the Invention
This invention relates to a thermal image transfer recording medium which has high thermal sensitivity and can yield images with high heat and abrasion resistances, and more particularly to a thermal image tranfer recording medium which can be used for printing images, for instance, on price tags for textile goods.
2. Discussion of Background
Conventionally known thermal image transfer layers (ink layers) of thermal image transfer recording media are as follows: (1) a thermal image transfer layer comprising an emulsified resin having a lowest film-forming temperature of 40.degree. C. or more as disclosed in Japanese Laid-Open Patent Application 63-57679; (2) a thermal image transfer layer comprising as its main component a copolymer of styrene, methylmethacrylate and butylacrylate as disclosed in Japanese Laid-Open Patent Application 62-23779; (3) a thermal image transfer layer, formed on a transparent protective layer composed of a styrene-methacrylate copolymer and a polyvinyl chloride resin, comprising a styrene-methacrylate copolymer, polymethacrylate, a polyvinyl chloride resin and a coloring agent as disclosed in Japanese Laid-Open Patent Application 62-179992; and (4) a thermal image transfer recording layer, formed on a transparent protective layer made of a chlorinated polyolefin resin, comprising a (meth)acrylate polymer and a coloring agent as disclosed in Japanese Laid-Open Patent Application 63-42891.
The conventional thermal image transfer recording media comprising the above thermal image transfer layers cannot yield images having sufficiently high resistance to heat. Therefore, when they are used for printing images, for instance, on a price tag for clothing, which is commonly attached to clothing before the clothing is hot-pressed, the images printed on the price tag are blurred. Moreover, the ink of the images stains the clothing and also the price tag itself.
Namely, resins having a lowest film-forming temperature of 40.degree. C. or more, which are used in the above-described thermal image transfer layer (1), are not necessarily high-heat-resistant. Therefore, images printed on a price tag attached to clothing by using the recording medium comprising such a resin are blurred when the clothing is hot-pressed at a temperature of approximately 100.degree. C., and the price tag sticks to the clothing.
On the other hand, a resin having a lowest film-forming temperature of less than 40.degree. C. is used, the thermal image transfer layer of the recording medium, when in the form of a rolled ribbon, sticks to the reverse side of the support which is in contact with the thermal image transfer layer in the roll even when preserved at room temperature. In other words, the so-called "blocking" occurs.
An emulsion of a resin having a high glass transition temperature, such as a polymethylmethacrylate resin, has a high lowest film-forming temperature. Therefore, a recording medium comprising such an emulsion in its image transfer layer cannot exhibit high thermal sensitivity. Moreover, images printed on a price tag attached to clothing by using such a recording medium are blurred, and the ink of the images stains both the clothing and the price tag when the clothing is hot-pressed at a temperature of 140.degree. C. or more.
Furthermore, in the case where a thermal image transfer recording medium comprises in its thermal image transfer layer a wax having a low melting point as a binder, images printed by the recording medium on a price tag attached to clothing are blurred, and both the clothing and the price tag are stained by the ink of the images when the clothing is subjected to hot pressing. Therefore, such a recording medium is not suitable for image-printing on price tags for clothing.
When the thermal image transfer layer of (2), (3) or (4) comprises a resin having a high glass transition temperature, it exhibits low thermal sensitivity and images transferred from the layer on a price tag attached to clothing is suffered from low resistance to hot pressing conducted at a temperature of 140.degree. C. or more. The thermal sensitivity can be improved by incorporating a resin having a low glass transition temperature, but doing so the resistance to hot pressing becomes worse.
In addition, the thermal image transfer layer (4) is formed on a protective layer made of a chlorinated polyolefin, so that images obtained from this layer cannot be expected to have high resistance to hot pressing.